New distributional records of two butterflies from Bangladesh: Insights into potential climate-driven range shifts

Uzzal Das, Avijit Dutta Borshon

During field surveys on butterfly taxa at Madhobkunda Eco Park, located in the northeastern region of Bangladesh, two species from the Hesperiidae family were recorded for the first time in the country. Particularly, a skipper butterfly, Pithauria marsena, Hewitson,1866 (Banded Straw Ace), was observed in December 2023, and a flat butterfly, Celaenorrhinus nigricans, de Nicéville,1885 (Small-banded flat), was observed in February 2025. Both species were identified based on their key morphological traits and have not been previously documented from Bangladesh. This represents the confirmation of the first record of these two species in Bangladesh, which falls well outside their previously known distribution ranges. These locations do not overlap with historical clusters, suggesting an actual range extension rather than random isolated sightings. We hypothesize that regional climate trends, together with the dispersal abilities of the species, are allowing them to expand into peripheral portions of their known ranges. Though single observations cannot confirm expanding populations, but a significant geographic gap between previous and current records suggests the possibility of undiscovered resident or gradually shifting range movements. Such range movements are becoming more common among tropical insects, as warming temperatures, shifting seasonal cycles, and microclimate shifts make new habitats suitable. Also new records of these butterflies highlight the ecological significance of Madhobkunda Eco Park and will help to enrich the known butterfly diversity of Bangladesh.